A tire vulcanization mold includes an exhaust mechanism. The exhaust mechanism discharges air remaining between a green tire and the mold and gas generated during vulcanization to the outside of the mold. Conventionally, a vent hole has often been used as an exhaust mechanism. However, when rubber flows into the vent hole during vulcanization, a spew is generated. Therefore, various exhaust mechanisms that do not generate a spew have been proposed (see Patent Documents 1 and 2, for example).
In the exhaust mechanism proposed in Patent Document 1, a multilayered blade is used to ensure sufficient ventilation. The multilayered blade is a folded thin plate having an end portion formed by bringing the ends of the plate together and the opposite end portion in which a large gap is formed. A block holds the multilayered blade in place. The block is fitted in a recessed pocket in a tire molding surface of the mold such that an exhaust chamber defined by the pocket and the block is formed. Air and gas are discharged into the exhaust chamber via a fine gap on the one end and a large gap on the other end of the multilayered blade. However, the exhaust mechanism requires steps of forming the pocket in the tire molding surface of the mold formed by casting; producing an assembly of the block holding the multilayered blade; and fitting the assembly in the pocket. Therefore, the exhaust mechanism of Patent Document 1 has a problem of increase in production time due to increase in the number of processing steps.
According to the invention described in Patent Document 2, when casting pieces that constitute a mold, molten metal is divided into a plurality of batches and then shot into a cast. The shots lead to the formation of a fine gap at a cast joint portion between the cast pieces due to solidification shrinkage of the molten metal. The gap serves as an exhaust passage. According to this invention, however, molten metal should be shot into a cast in a plurality of times, resulting in a problem of increase in production time due to increase in the number of processing steps.